Researchers chase pollution plumes across Pacific Ocean
during PACDEX

When it comes to global air pollution, what goes around comes around. Because prevailing winds blow from west to east around Earth’s midlatitudes, air pollution originating in North America drifts across the Atlantic Ocean to Europe, while Asia’s emissions wind up in North America.

Starting this month, a team that includes about a dozen NCAR researchers is crisscrossing the Pacific Ocean in the Gulfstream-V, chasing giant plumes of pollutants and natural dust that journey from Asia to the West Coast. Called PACDEX (PACific Dust EXperiment), the field campaign runs through early June.

Kurt Zrubek (left) and Bob Beasley, both from EOL, fit a vertical pylon to the underside of the G-V’s wing. The pylon is part of an external wing store system that will allow the research team to fly cloud physics instruments, video cameras, laser air motion sensors, and more under the wing.

As Asia’s economies boom, scientists are increasingly turning their attention to these traveling plumes, which pack a combination of industrial emissions (soot, smog, trace metals) and dust from storms in Central Asia’s Gobi Desert. The plumes are among the largest events on Earth involving dust and pollutants, so great in scope that scientists believe they might affect clouds and weather as they travel across the Pacific. The plumes also block some of the Sun’s radiation, which has implications for global climate change.

“PACDEX will give us a window on what happens to these plumes as they cross the Pacific Ocean and interact with clouds and solar radiation,” explains Jeff Stith (EOL), a principal investigator on the project. “This information is needed if we are to accurately model and predict the effects of these plumes on weather and climate.”

To study the plumes as they drift across the Pacific, the team will make multiple flights in the G-V between Japan and Seattle, with refueling stops in Alaska. Researchers aboard will use instruments to measure dust and pollutants at levels in the atmosphere ranging from a mere 500 feet above the ocean
to more than 45,000 feet. Although scientists have gathered information about the giant plumes during past field projects, the G-V’s long range (6,000 miles) and ability to fly at high altitude will enable them to follow dust and pollution across the Pacific to study
how the particles interact with clouds in the upper troposphere (the lowest portion of the atmosphere, starting at Earth’s surface).

These canisters, which are coated with a mixture that simulates ice shapes, are part of the external wing store system that attaches to the underside of the G-V. With the help of a program called LEW Ice, engineers designed the ice shapes for test flights to show that the wing stores will be safe during any icing conditions that may be encountered.

The plumes generally take several days to cross the Pacific. Some of the microscopic particles of dust and pollutants in them serve as nuclei for the formation of cloud droplets and ice crystals and can eventually grow large enough to produce rain or snow. Since Asian plumes reach as far as North America, it is important to know how many of these nuclei are present in the plumes if scientists are to determine whether there is a potential impact on the continent’s weather.

Scientists believe that the dust and pollutants also contribute to the whiteness of cloud tops. As clouds become whiter, they tend to reflect more sunlight back into space, preventing it from reaching Earth. Because this can partially counteract the impact of greenhouse gases in the atmosphere and reduce the extent of global warming, scientists who study climate change are striving to quantify the impacts of clouds on climate.

“We know that clouds, dust, and pollutants are important players in the climate system,” says Phil Rasch (ESSL/CGD), a climate scientist working on PACDEX. “We also know that they interact with each other. The particles change the cloud properties, and the clouds change the particles. PACDEX provides an opportunity to improve
our understanding of how that interaction works.”

The G-V has been outfitted with an array of new instruments for measuring clouds and for bringing dust and pollutants into the aircraft for study. In one experiment, for example, researchers aboard the plane will capture ice particles from clouds, evaporate them, study the residue, and then try to recreate the particles in a moistened chamber to mimic the temperature and moisture conditions that enabled the original particles to form.

NCAR is partnering with Scripps Institution of Oceanography for PACDEX, with additional collaborators from NASA, NOAA, the Naval Research Laboratory, and a number of universities across the United States and in Japan, China, and Korea.